In conventional valves of the type used in swimming pool or other water filtration systems and the like, cost and corrosion resistance are of paramount importance. Typically these valves will contain an influent port, an effluent port, and a drain port. Typically these valves are also constructed of cast metal parts, which are expensive to manufacture and are subject to considerable corrosion. U.S. Pat. Nos. 2,639,728; 4,128,110; and 21,332 disclose typical valve structures.
The low strength of unreinforced injection molded plastics typically is in the range of 4,000 to 10,000 psi tensile strength compared to 30,000 psi to 180,000 psi for steel. As a result, it has been difficult to manufacture an unreinforced plastic valve of sufficient strength to withstand the thrust forces of the valve actuator which reach 2,500 lbs in a 6" diameter valve, for example.
Some attempts have been made to construct components of valves out of less expensive, less corrosive plastic members. U.S. Pat. No. 4,262,698 describes one such attempt. The valve structure shown in U.S. Pat. No. 4,262,698 requires specially constructed valve seats and an expensive and complicated valve disk of plastic and steel.